A matrix substrate constituting a flat image display element such as a liquid crystal panel is an electric circuit board in which various electric circuit elements, such as a pixel electrode constituting a unit of image display, a switching element for applying a predetermined electric charge to the pixel electrode and a metal line are formed on the inner surface.
In the vicinity of an end portion of the matrix substrate constituting the liquid crystal panel, electrode terminals are provided at tips of lead-out lines that are led out from the metal lines formed in a display region where images are displayed, and a flexible substrate (FPC: Flexible Printed Circuit) is connected to these electrode terminals. Thus, various signals for displaying images and a power supply voltage for activating the matrix substrate as the electric circuit board are supplied from peripheral circuit boards other than the liquid crystal panel 10.
The lead-out lines formed on the matrix substrate include a power supply line for supplying a power supply potential for activating the electric circuit elements formed on the matrix substrate and a ground line for connecting ground potentials in an electric circuit formed on the substrate. Since the large amount of current flows through the power supply line and the ground line, it is necessary to reduce electrical resistance values of these lines. Because of this, the power supply line and the ground line generally are formed wider than other signal lines, and not all the lead-out lines have the same line width. On the other hand, the electrode terminals formed on the matrix substrate are formed to have the same line width and the same pitch.
The matrix substrate and the flexible substrate are connected as follows: an anisotropic conductive film (ACF) in which conductive microparticles are mixed in an adhesive resin base material is attached to an connection portion of either of the matrix substrate and the flexible substrate; connection terminals and their corresponding electrode terminals are aligned to overlap with each other; and the overlapped substrates are pressed with a predetermined pressure. Thus, the conductive particles in the anisotropic conductive film connect the connection terminals of the flexible substrate and the electrode terminals of the matrix substrate electrically, and the adhesive resin that is the base material joints the flexible substrate and the matrix substrate physically, thereby connecting both the substrates electrically and physically at the same time.
FIG. 7 is a partial enlarged plan view showing the connection portion between the matrix substrate 2 of the liquid crystal panel and a flexible substrate 50 in the conventional liquid crystal display device. Note here that, for the sake of simplicity, an illustration of the anisotropic conductive film connecting the flexible substrate 50 and the matrix substrate 2 is omitted.
As described above, the electrode terminals 6 formed on the matrix substrate 2 have the same line width and the same pitch. On the other hand, the lead-out lines 4 (4a, 4b, 4c) have different line widths depending on the application. For example, as for the electrode terminal 6 of a narrow lead-out line 4a used as a signal line for example, one electrode terminal 6 is connected to one lead-out line 4a. As for the electrode terminal 6 of a slightly wide lead-out line 4b used as a power supply line for example, two electrode terminals 6 are connected to one lead-out line 4b. As for the electrode terminal 6 of an even wider lead-out line 4c used as a ground line for example, three electrode terminals 6 are connected to one lead-out line 4c. 
In the conventional flexible substrate 50 connected to the matrix substrate 2, an end portion of a wiring pattern 52 formed on a base film 51 is an exposed region 54 from which a protection layer 53 formed on the surface is removed. A portion of the wiring pattern 52 exposed in the exposed region 54 is a connection terminal 55. Note here that since the flexible substrate 50 is connected to the matrix substrate 2 in such a manner that the exposed connection terminals 55, from which the protection layer 53 has been removed, are opposed to the electrode terminals 6, the base film 51 of the flexible substrate 50 is positioned on a most frontward side, the protection layer 53 is positioned on a most backward side, and the wiring pattern 52 is positioned between the base film 51 and the protection layer 53. Further, the connection terminals 55 are formed to have the same pitch as the electrode terminals 6 to be connected, the connection terminals 55 of the conventional flexible substrate 50 have the same line width and the same pitch.
Note here that, in order to absorb an alignment error between the electrode terminals 6 and the connection terminals 55 during the connection operation of the matrix substrate 2 and the flexible substrate 50, generally, as shown in FIG. 7, the connection terminals 55 of the flexible substrate 50 made of low-resistant metal foils are designed to be narrower than the electrode terminals 6 formed as metal films on the matrix substrate 2.